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    Home > Coatings News > Coating Additive Market > Interpreting the "code" of thickeners and wetting dispersants for water-based coatings (2)

    Interpreting the "code" of thickeners and wetting dispersants for water-based coatings (2)

    • Last Update: 2020-09-19
    • Source: Internet
    • Author: User
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    . 2. The action of water-based coating thickener and wetting dispersant
    Cellulose thickener cellulose thickener thickener thickener thickener thickener thickener thickener thickening agent is the main chain of hydrophobic water and surrounding water molecules through hydrogen bonding, improving the fluid volume of the polymer itself, reducing the space for particles to move freely, and then improving the system viscosity. It can also go through the molecular chain around the completion of the progress of viscosity, as shown in static and low shear has a high viscosity, in high shear for low viscosity. This is because at static or low shear speeds, cellulose molecular chains are out of order and make the system highly viscous, while at high shear speeds, molecules are placed in an orderly manner in the direction of activity, making it easy to slide against each other, so the viscosity of the system decreases. Polyacrylic thickener its thickening agent is thickener dissolved in water, through the same-sex electrostatic refractive reprice of the root ions, the molecular chain from spiral to rod, and then improve the viscosity of the water phase. Other than that, it forms a mesh layout through a bridge between latex grains and pigments, increasing the viscosity of the system. In the molecular layout of the combined polyurethane thickener, hydrophobic and hydrophobic groups are introduced, so that they show the certainly the properties of the appearance of the active agent. When its aqueous solution concentration exceeds a certain concentration, it forms a beam, which is combined with polymer particles to form a mesh layout, which increases the viscosity of the system. On the other hand, a molecule with several glue bundles, reduced the migration of water molecules, so that the viscosity of the water phase is also improved. This thickener not only affects the fluidity of the coating, but also has an effect on each other with adjacent latex particles, which can lead to latex layering if it is too strong. Inororated thickener bento is a layered silicate, water absorption after swelling constitutes a floc-like substance, with outstanding suspension and dispersion, with the appropriate water linked to the collosome, in the water can release charged particles, increase the system viscosity.
    wetting is actually a surface replacement process, the wetting agent molecule removes the air displacement from the pigment surface, thereby reducing the interface between the liquid/solid, and enhancing the pigment affinity to improve dispersion efficiency and dispersion stability. In fact, the wetting dispersion and stability of pigment fillers are three inseparable processes. The main purpose of wetting is to reduce the interface pressure of the substance, many powder pigments if not wet to reduce their surface pressure will lead to their long dispersion time or even poor dispersion; Dispersion is the process of separation of powder pigment polymers under the action of external forces. Stability is the process by which flocculation does not occur after the powder pigment is dispersed. The mechanical dispersion of the pigment block can be achieved by high-speed dispersion machine, sander and three-roll grinder. Tightly bonded particles will be crushed to obtain a certain fine pigment, the decisive step of which is to stabilize the dispersed particles by adding a dispersant. In order to fully disperse the pigment in the coating system and form a stable system, the following basic conditions need to be met: First, the first pigment filler can be well moisturized by the medium; Second, the polymer produced by the adhesion of primary pigment particles must be dispersed; third, the good dispersion system obtained must be stable, that is, the secondary cladding must be suppressed, so that the pigment dispersion must reach a stable state, the prerequisite is that the wetting dispersant must be firmly adsorbed on the surface of the pigment particles to form an electrical charge or spatial resistance effect, so that the dispersion is in a stable state.
    Surfactants are composed of hydro-based and oil-dependent base, when in contact with the solid surface, the hydro-oil base adheres to the solid surface, the hydro-hydraulic base extends outward into the liquid, so that the liquid on the solid surface to form a continuous phase, which is the basic principle of wetting action. Wetting agent is the structure with hydro-based, oil-based two groups of surfactants, it can reduce the interface between the liquid and solid surface pressure, so that the solid surface is easy to wet by the liquid, so that latex and pigment surface to fully contact. Dispersant is to achieve the full and stable dispersion of wet pigment particles and improve the suspension performance of solid particles in liquid. Commonly used dispersants are divided into inorganic dispersants and organic dispersants. Inorganic dispersants include phosphates, silicates, etc., the most used is sodium hexa-biased phosphate; Usually organic, inorganic two types of dispersant compound effect is better. Dispersant is an interface active agent with opposite properties of both oil-friendly and hydro-hydroactive properties in a molecule. It can be dispersed among the inorganic and organic pigment particles that are difficult to dissolve in liquids, and can also prevent the subsidion and condensation of solid particles, forming the necessary pharmaceutical agents for stable suspension. Dispersion agent action: adsorption to the surface of solid particles, so that the condensed surface of solid particles easy to moisturize. Polymer-type dispersants form an adsorption layer on the surface of solid particles, which increases the charge on the surface of solid particles and increases the reaction force between particles that form three-dimensional obstructions. So that the surface of solid particles form a dual molecular layer structure, the polar end of the outer dispersant and water have a strong affinity, increasing the degree of moisture of solid particles, solid particles between electrostatic refruffs away; The dispersants used in water-based coatings must be water-soluble, and they are selectively adsorbed to the powder-water interface. At present, commonly used is anion type, they ionized in water to form anion, and has a certain amount of surf activity, by the surface of the powder adsorption. Powder particle surface adsorption dispersant after the formation of a double electron layer, anions by the particle surface tightly adsorbed, known as surface ions. Ions with opposite charges in a medium are called antiions. They are absorbed by surface ions by electrostation, and a portion of the anti-ions binds more closely to particles and surface ions, which are called bound anti-ions. They become moving wholes in the medium, with a negative charge, while another part of the anti-ion is surrounded by what is called a free anti-ion, forming a diffusion layer. This creates a double layer between the surface ions and the antiions. The negative and diffusion layers of the particles are positively charged to form a double-electric layer, called the dynamic power level. A double electron layer formed between all anions and cations, corresponding to the likely likely likely to be.
    the dispersion of the action is the dynamic power level rather than the thermal momentum, the dynamic power level charge is not balanced, there is charge rejection phenomenon, and the thermoelectrelectration is the phenomenon of charge balance. If the concentration of anti-ions is increased in the medium, and the free anti-ions in the diffusion layer will be forced to enter the bound anti-ion layer due to electrostatic rebuke force, so that the double-electron layer is compressed, the dynamic power level drops, when all free anti-ions become bound anti-ions, the dynamic power level is zero, called isoelectronic point. The formation of a stable dispersion system, in addition to the use of electrostitive rejection, i.e. the absorption of negative charges on the surface of particles mutually exclusive, in order to prevent the adsorption/accumulation between particles and the final formation of large particles and layering/sinking, but also to use the theory of spatial bit resistance effect, that is, when the absorbed negative charge particles close to each other, so that they slide each other staggered, such space resistance of the surface active agent is generally non-ionized surface active agent. Flexible use of electrostitive rejection with the theory of spatial bit resistance can constitute a highly stable dispersion system. Polymer adsorption layer has a certain thickness, can effectively block the particles from adsorption, mainly rely on polymer solvent layer, when the surface of the powder adsorption layer up to 8 to 9nm, the repulsion between them can protect particles from flocculation. So polymer dispersants are better than ordinary surfactants..
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